The modified Duke criteria for infective endocarditis include 'minor' criteria. A patient has fever of 39.2°C, a new regurgitant murmur, two separate blood cultures positive for Streptococcus viridans, and an echocardiogram showing a mobile vegetation on the mitral valve. How many major Duke criteria are satisfied in this patient?

• A One major criterion — positive blood cultures only
• B Two major criteria — positive blood cultures (viridans streptococcus from two separate cultures) and endocardial involvement (vegetation on echocardiogram) ✓
• C Three major criteria — blood cultures, echocardiogram, and new murmur
• D One major criterion — echocardiogram only; blood cultures are a minor criterion for viridans streptococci

Explanation

Under the modified Duke criteria, the major criteria are: (1) positive blood cultures with typical organisms (Viridans streptococcus, S. bovis, HACEK group, S. aureus, or enterococcus without primary focus) from two separate cultures qualifies as a major criterion; and (2) evidence of endocardial involvement — a positive echocardiogram showing an oscillating intracardiac mass (vegetation) or new valvular regurgitation. Both are major criteria here, satisfying the 2 major criteria threshold for definite IE. A new regurgitant murmur not on echo is a minor criterion; however, echo showing the vegetation already covers endocardial involvement.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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